Electrically powered outdoor lighting systems are used to illuminate pathways, yards, parks and other like outdoor areas for security purposes. Commonly, such lights are connected to public utility systems or similar sources of electrical power and are controlled by preset timing devices to illuminate desired areas at nightfall and automatically turn off at a predetermined time, for example, prior to daybreak.
Many conventional lighting devices require extensive cabling, suitable timing mechanisms and the like, and are thus relatively expensive to install and maintain. In addition, such lighting devices utilize electric power generated in a conventional manner such as by burning fuel. Burning fuel contributes to contamination of the environment and depletion of existing fuel resources.
More recent lighting devices include self-contained solar powered devices which utilize photovoltaic cells to charge batteries which, in turn, activate a light source contained therein, in the absence of sunlight. Such self-contained devices are desirable because they are relatively inexpensive and maintenance-free.
A plurality of such solar powered lamps can be disposed in any predetermined arrangement outdoors to illuminate or delineate desired areas. For example, a particular area, such as a pathway, may be easily delineated so that a person, even in complete darkness, can follow the pathway without the necessity of producing overhead illumination.
Although prior solar powered illumination devices are known to serve their purpose, they have not proven entirely satisfactory. During a certain period of time approaching sundown, when the level of ambient light is such that illumination is not required, for example when the ambient light decreases to a level between 600-1500 LUX, the solar powered lamps are known to turn on partially and slowly. This is undesirable because current is drawn from the batteries for a substantial period of time during which illumination is not necessary, thereby significantly shortening the run time for the lamp.
In addition, the control circuitry of the solar powered lamps typically causes a significant drain on the battery, for example between 8-30 mA, even during times when the solar powered lamp is operating and illumination is required. Again, this considerably shortens the run time of the lamp.
Moreover, in situations where a plurality of such solar powered lamps are used, erratic illumination often occurs. The lamps illuminate at different times, for example, sometimes at intervals as much as 30 minutes apart, because manufacturing tolerances inherent in individual components of these prior devices affect their operation. Such irregular illumination is inefficient, unattractive and consequently undesirable.